Solid fuel propellant containing surface passivated beryllium



United States Patent of Delaware No Drawing. Filed Feb. 25, 1963, Ser. No. 260,865 20 Claims. (Cl. 149-3) This invention relates to improvements in solid fuel propellants.

An object of the present invention is to provide a solid fuel propellant having improved physical properties over other solid fuel propellants, such as greater density and more even burning action. Another object of the invention is to provide an improved solid fuel propellant having the stated improved physical properties and consisting of a resin, particularly a synthetic resin, an oxidizing agent, and a surface treated metal powder.

More specifically an obejct of the invention is to provide a solid fuel propellant of the character stated in the preceding paragraph in which the metal powder of the mixture is in a passive state.

Still more specifically, an object of the invention is to provide a solid fuel propellant comprising a resin, an oxidizing agent, and beryllium metal powder in which the metal particles have received a surface treatment of a character to render the metal passive and which passivated beryllium particles have a reduced polymerization effect upon the resin, resulting, after addition of a curative agent, in a propellant of greater density and a more desirable burning action.

The surface treatment of beryllium powder in accordance with the present invention and as hereinafter described, results in rendering the powder more inert relative to the resin with the further result that a more readily controlled propellant composition is obtained.

As an example of the unexpected results obtained by the use of beryllium powder for producing a solid fuel propellant, in accordance with the present invention, and wherein the beryllium powder has received a surface treatment, rendering the same chemically more inert, a solid propellant prepared with the resin polybutadiene acrylic acid (PBAA) formulations, for example, containing untreated beryllium metal powder, requires a reficiency of curative agents because of the polymerization effect caused by the beryllium powder. This results in a sacrifice of physical properties of the solid propellant, causing it to be slightly more embrittled. This embrittlement is due to a localized polymerization of the resin surrounding the surface of each beryllium particle. In addition there is present a general microscopic porosity throughout the propellant.

By the empolyment of beryllium metal powder in which the particles have received surface treatment in accordance with the present invention, and in the same formulation, the addition of a greater quantity of curative agent is required and the result is the formation of a denser propellant with more desirable physical properties and an increased flexibility in the formulation.

One procedure for treating the beryllium metal powder comprises subjecting the powder to the action of an aqueous solution mixture of potassium dichromate, K Cr O7, and phosphoric acid, H PO whereby the metal particles pick up, or acquire, a surface coating complex of chromium and phosphorous, and the metal particles become passive, or are in a passive state.

As an illustration of the passivity effect produced by surface treating the beryllium metal powder by the foregoing procedure, the following tests were made:

Equal parts by weight of polybutadiene acrylic acid polymer (PBAA) and fine, untreated beryllium metal powder, were mixed together. This mix, with the untreated beryllium powder, polymerized fully within twenty four hours at room temperature.

A second mix, prepared with beryllium metal powder surface treated as described, remained fluid after standing at room temperature over 2 months.

In accelerated testing at 110 C. (230 F.), mixes with untreated powders polymerize fully after a few hours, whereas mixes prepared with the surface treated beryllium powders are fluid after twenty four hours and retain their fluidity after standing at room temperature an additional month.

In the carrying out of the surface treatment procedure hereinabove broadly set forth, a stock solution is made, composed of equal parts by volume of concentrated phosphoric acid and a saturated aqueous solution of potassium dichromate. Different dilution-s of the stock solution with water may be employed and will produce desirable surface passivity of the beryllium metal powder as determined by the above described tests with PBAA.

The activity of the reaction resulting from mixing the stock solution with water decrease as the degree of dilution of the stock solution increases. As an example, use may be made of a mixture of equal parts by volume of water and stock solution which gives an active reaction with beryllium powder and dilutions of as much as 50 parts water and 1 part stock solution, while exhibiting a very mild reaction with beryllium powder, gives to the powder very excellent surface passivity.

Using a dilution of 20 parts water to 1 part by volume of the stock solution results in a pick up of from .03 to .5 percent chromium and .01 to .10 percent phosphorous in the surface treated powder, depending on the particle size of the powder.

Another stock solution employed for effecting the desired surface treatment consists of a saturated aqueous solution of potassium dichromate which when diluted with not more than 5 parts by volume of water results in excellent surface treatment passivity. Using a one to one dilution of this solution with water results in a chromium pick up of from .2 to .9 percent.

While it is not clearly understood what exact mechanism is involved in connection with the surface treatment which results in the passivity of the metal particles, X-ray diffraction studies indicate that the surface treated powders contain less beryllium oxide than the untreated beryllium powders.

While the chromium coating received by the powder particle may be of varying thickness, it has been calculated that a monomolecular coating of chromium on the surface of a 4 micron particle size beryllium metal sphere would result in .101 percent chromium.

As a more specific illustration of the process of the invention the following example is given:

Five gallons of surface coating solution consisting of 1 pint of reagent grade percent phosphoric acid, 1 pint of saturated solution of potassium dichromate and 4% gallons of water, cooled to room temperature, was placed in a stainless steel vessel, fitted with an agitator. 6 lbs. of nominal 10 micron beryllium subsieve powder was gradually added over a period of ten minutes, with agitation, and the agitation was continued an additional twenty minutes.

The slurry was filtered and the filter cake was washed with 5 gallons of water and refiltered.

The contained water was removed by washing with acetone followed by a hydrocarbon solvent such as Stoddard solvent, and the resulting filter cake was dried under vacuum to produce the surface treated powder.

The solution of the foregoing example gives a dilution of the acid-dichromate mixture of about 1 to 19. The

reaction with the beryllium powder is relatively mild and gives a surface coated powder having excellent passivity as determined by the hereinbefore described test with PBAA.

Another chromium containing solution may be employed, made up from a stock solution consisting of chromium anhydride, CrO and phosphoric acid.

A saturated solution of the chromium anhydride is mixed with an equal volume of concentrated phosphoric acid to make the stock solution. A dilution of 1 part of this stock solution with 20 parts of water, used for treating the beryllium metal powder, gives powder particles having excellent surface passivity, as determined by the described test. W V V The surface treated beryllium powder is mixed with the selected resin and an oxidizing agent such as ammonium perchlorate for the production of a solid fuel propellant having the stated characteristics. Such mixtures of an oxidizer, or oxidizing agent, and a fuel are commonly referred to, by those skilled in the art, as composite propellants.

The resin or other polymen'zable material may be the polybutadiene acrylic acid, polyurethane, and double base propellants such as nitroglycerine-nitrocellulose.

While reference has been made in the example given, to beryllium subsieve powder it is to be understood that the invention is applicable to the use of powders of particle size in the range of from 1 to 100 microns.

I claim:

1. A solid fuel propellant comprising an oxidizing agent, a polymerized resin and beryllium metal powder particles dispersed therethrough and separated from contact with the resin by a coating of chromium on the particles, whereby polymerization action of the metal on the resin is inhibited.

2. The invention according to claim 1, wherein the resin is polybutadiene acrylic acid.

3. A solid fuel propellant comprising an oxidizing agent and a polymerized resin having dispersed therethrough beryllium metal powder particles carrying a passivating surface layer of a chromium-phosphorous complex.

4. The invention according to claim 3, wherein the resin is polybutadiene acrylic acid.

5. A solid fuel propellant consisting of an oxidizing agent and a polymerized resin having dispersed therethrough beryllium metal powder particles passivated by a coating of another metal which inhibits polymerization of the resin by contact between the latter and the beryllium.

6. A solid fuel propellant consisting of an oxidizing agent and a polymerized resin having dispersed therethrough beryllium metal powder particles carrying chromium and phosphorous on the surface thereof.

7. The process of producing a solid fuel propellant, which comprises effecting deposition of chromium on particles of beryllium metal powder, mixing the chromium carrying metal powder particles with a resin and an oxidizing agent, and then adding a setting agent to polymerize the resin to a solid state.

8. The invention according to claim 7, wherein the resin is polybutadiene acrylic acid.

9. The process of producing a solid fuel propellant which comprises subjecting beryllium metal powder to the action of a solution containing a chromate, maintaining the beryllium powder in a solution for a suificient time to bring about deposition of chromium on the particles of the powder, filtering the slurry to remove the powder, washing the powder and refiltering, removing the contained water from the powder and drying the same to obtain chromium surfaced powder particles, then adding such particles to a resin and an oxidizing agent, and then adding a setting agent to polymerize the resin to a solid state.

10. The invention according to claim 9, wherein the resin is polybutadiene acrylic acid.

11. The process of producing a solid fuel propellant, which comprises subjecting beryllium metal powder to the action of a chromate and phosphoric acid in aqueous solution, maintaining the beryllium powder in the solution for a sufiicient time to bring about deposition of chromium and phosphorous on the particles of the powder, filtering the slurry to remove the powder, washing the powder and refiltering, removing the contained water from the powder and drying the same to obtain chromium-phosphorous surfaced powder particles, then adding such particles to a resin containing an oxidizing agent, and then adding a setting agent to polymerize the resin to a solid state.

12. The invention according to claim 11, wherein the W resin is polybutadiene acrylic acid.

13. The invention according to claim 11, wherein the resin is polybutadiene acrylic acid and wherein the beryllium powder particles are surfaced with a coating of from about .03 to about .5 percent chromium and from about .01 to about .10 percent phosphorous pickup in the metal powder.

14. The process of producing a solid fuel propellant, which comprises the preparation of a stock solution consisting of equal parts of a saturated aqueous solution of potassium dichromate and percent phosphoric acid, then preparing a dilution of the stock solution in the range of from 1 to l, to 50 parts water, then adding beryllium metal powder to the dilution and maintaining the same therein with agitation for approximately 10 to 30 minutes, then filtering the slurry to obtain a filter cake, washing the filter cake and refiltering, then removing contained water by washing with acetone followed by a hydrocarbon solvent, then drying the resulting filter cake to obtain beryllium powder particles carrying a chromium and phosphorous deposit on the surface thereof, then adding the so treated beryllium metal powder particles to polybutadiene acrylic acid, and then adding an oxidizing agent and a setting agent to polymerize the resin to a solid state.

15. A propellant consisting of surface treated passivated beryllium metal powder particles combined in and dispersed through a composite type propellant fuel mixture.

16. A propellant consisting of surface treated passivated beryllium metal powder particles combined in and dispersed through a double base solid propellant.

17. A propellant consisting of surface treated passivated beryllium metal powder particles combined in and dispersed through a mixture of polyurethane and an oxidizing agent.

18. A solid fuel propellant comprising a mixture of an oxidizing agent and polybutadiene acrylic acid resin and having dispersed therethrough beryllium metal particles on which is a surface layer of another metal which separates the beryllium metal particles from contact with the resin and inhibits polymerization of the resin by the beryllium metal.

19. A solid fuel propellant consisting of a composite type propellant having dispersed therethrough beryllium metal powder particles carrying chromium and phosphorous on the surface thereof.

20. A solid fuel propellant having dispersed therethrough beryllium metal powder particles carrying a metallic passivating surface layer which inhibits polymerization of the propellant adjacent the surface of each passivated beryllium particle.

References Cited by the Examiner UNITED STATES PATENTS 2,970,898 2/1961 Fox 149-76 3,002,830 10/1961 Barr 149-19 3,070,469 12/1962 Jenkins l495 CARL D. QUARFORTH, Primary Examiner. 

1. A SOLID FUEL PROPELLANT COMPRISING AN OXIDIZING AGENT, A POLYMERIZED RESIN AND BERYLLIUM METAL POWDER PARTICLES DISPERSED THERETHROUGH AND SEPARATED FROM CONTACT WITH THE RESIN BY A COATING OF CHROMIUM ON THE PARTICLES, WHEREBY POLYMERIZATION ACTION OF THE METAL ON THE RESIN IS INHIBITED. 